1. Field of the Invention
This invention relates to a spark-ignition type internal combustion engine.
2. Description of Related Art
Internal combustion engine development is aimed at reducing exhaust-gas and noise emissions and lowering fuel consumption. Presently, the diesel type internal combustion engine has better fuel consumption than spark ignition engines. However, the spark-ignition type engine has advantages over the diesel engine, particularly with regard to particle and noise emission. It also has a higher specific power output potential.
Conventionally, the engine""s combustion chamber is supplied with a homogeneous stoichiometric or rich fuel/air mixture so that the fuel/air mixture is ignited by the spark plug at the desired ignition point. Typically, during part-load operation the quantity of fuel and air are reduced by throttling. Throttling losses result in higher fuel consumption in a spark ignition engines than in a diesel engine. A diesel engine normally operates with a leaner fuel/air mixture than a spark ignition engine. It is desirable to provide a mixed operating mode in a spark ignition type engine to achieve both high torque characteristics and high power output. Thus, during a lower and medium speed range of engine operation a stratified-charge mode is desirable combined with a largely unthrottled air supply strategy. During a higher-load and higher speed range of engine operation, a homogeneous stoichiometric fuel/air mixture is desirable.
To produce a homogeneous stoichiometric fuel/air mixture desired for a higher-load and higher speed range of engine operation, fuel injected directly into the combustion chamber must be introduced at an early stage in the cycle, even as early as the latter portion of the intake suction portion of the engine cycle. Resultantly, the energy and volume of the air intake is utilised efficiently to create a high mean pressure and therefore a high torque characteristic. To produce a stratified-charge mode desired for a lower and medium speed range and part load mode of engine operation, fuel injected directly into the combustion chamber may be introduced into the combustion chamber relatively late during the compression portion of the engine cycle.
In normal operation or practice, vehicle engines are usually operated in a part-load and medium speed operational range. Therefore, a characteristic map or chart of engine operations should coincide with the characteristics associated with operation under a stratified-charge mode with its advantageous fuel consumption characteristics. However, there are good reasons to limit the operation in the stratified-charge mode of operation. For example, operation with a mean indicated pressure higher than about four bar can produce increasing emissions of soot particles. This occurs because there is insufficient time for complete evaporation under operation involving a large mass of fuel. Accordingly, the maximum useful operational range for stratified-charge characterised by a relatively late fuel injection is limited by speed and load variables. Furthermore, high exhaust-gas recirculation rates are necessary in order to lower the raw emissions of nitrogen oxides during engine operation in these relatively high speed and load ranges. High exhaust-gas recirculation rates leads, in turn, to increased hydrocarbon emissions and to a rise in fuel consumption.
In engines with direct injection of fuel, there are three combustion processes or methods available. A distinction is made between the three basic patterns which are: a jet-controlled method; a wall-controlled method; and an air-controlled method. Several factors are important with all three methods as follows: the properties of the fuel injector or jet; the geometry of the combustion chamber; and the air charge movement.
The jet-controlled method is characterised by a close spatial relationship between the fuel injector and the spark plug or plugs. The cloud of fuel injected into the combustion chamber forms a relatively compact area or zone, to which a quantity of air is introduced. Typically, the movement of the air is in a swirling pattern about an axis of the engine cylinder. The spatial arrangement of the fuel injector and the spark plug or plugs in the combustion chamber must be coordinated carefully to control the stratification profile.
With the wall-controlled method, the fuel/air mixture is formed and controlled by utilising adhesion of fluid to the walls of the combustion chamber and cylinder combined with subsequent separation.
The air-controlled method is based on the principle of transporting injected fuel to the spark plug by the movement of the air charge into the combustion chamber while at the same time actively mixing the air into the fuel cloud. The objective is to achieve a flattening of the stratification profile, so that formation of an extensive rich mixture zone is prevented.
In all three methods, essential factors for good part load and medium speed operation are: the charge movement; the air movement; the characteristics of any recirculated exhaust gas; and turbulence generation. At low engine speeds, an insufficient movement of the charge leads to an inadequate state of mixture preparation because of relatively low velocity between the inlet air flow and the flow from the injector. This typically produces increased emissions of carbon monoxide, hydrocarbons and soot.
The reference, JP-A 62-48927, discloses a spark-ignition internal combustion engine which has two inlet valves for each cylinder and with separate inlet passages leading to each valve. The first passage is orientated with respect to the combustion chamber to lead thereto in an essentially straight path and the second passage is oriented with respect to the combustion chamber to produce an air swirl pattern. A regulating valve associated with the first passage can be closed during a part-load range or engine mode to produce a swirl pattern of the intake air. By this method of intensifying and directing the air flow, the engine can be operated in a lean fuel/air mixture mode. Furthermore, in this mode the emissions of carbon monoxide, hydrocarbons and soot are markedly reduced. Furthermore any increase in nitrogen oxide emissions as a result of the intensified combustion can be compensated by increasing the degree of exhaust-gas recirculation. In a higher part-load or speed range using an essentially homogeneous charging process with a lean fuel/air mixture or an air ratio equal to one and using substantial exhaust-gas recirculation, the objective is to gain a relatively high charge movement so that a dilution tolerance with an air ratio xcex greater than 1.5 can be obtained.
The primary object of the invention is to achieve a desirable charge movement over a wide speed range and/or load range of the engine along with a low-throttle loss part-load range.
According to the invention, a charger mechanism includes a connecting duct or passage between the first and the second passages. A regulating device is arranged in the connecting duct to apportion the air charge through the two inlet passages according to operating parameters. In this embodiment, the controlled air charge is utilised not only to raise the power output of the engine, but also to intensify and control charge movement. As a result, the engine operating range utilising the advantageous stratified charge mode is enlarged, especially into the upper part-load operating range or mode. Accordingly, it covers wider ranges of the useful driving conditions.
The intensification of the charge movement tends to inhibit undesirable knocking behaviour of the engine. Furthermore, due to the higher mass throughput under part load and consequently lower throttling, the dynamic response behaviour of the engine is appreciably improved, particularly as compared to an engine utilising intake manifold injection rather than direct injection. In a direct injected engine, the increased mass throughput can be utilised with little or no throttling and is not characterised by a time delay as with indirect injection. Moreover, because of a desired excess of air, there is the possibility of providing a second injection of fuel during the expansion phase of the cycle in order to increase exhaust gas energy to be utilised to drive a turbocharger or to rapidly heat-up a catalytic converter. Finally, in the stratified charge mode under a falling load, the higher mass throughput produces a temperature decrease which has an advantageous effect on the temperature profile for a DENOX type catalytic converter. This desirable effect may be further assisted by utilising a charge-air cooler or innercooler in the charge-air intake line.
Desirably, a centrifugal compressor or a volumetric compressor may serve as an air charger or supercharger. The charger may be driven by an exhaust gas turbine or be mechanically connected to the engine or be independently powered by an electric motor. An exhaust gas shock-wave type compressor could also be used. The air charger is directly connected to the first inlet passage by a charge air line which can include the charge air innercooler. No throttle valve is provided in the charge air line. The previously mentioned regulating device arranged in the connecting passage between the first and second inlet passages serves to influence the charge movement not for conventional quantity or flow regulation. The load related operation of the engine is controlled by means of the fuel injected per work cycle.
According to one refinement of the invention, the second inlet passage is connected to atmosphere via an intake line. In the intake line, a one-way or non-return valve is placed upstream of the connecting passage and a throttle valve is positioned further upstream from the one-way valve. The non-return valve prevents a flow of charge air to being expelled away from the engine. In a homogeneous charge mode, the connecting passage is selectively closed by the regulating device and the engine can take-in air through the second inlet passage, the non-return valve, and the throttle valve with the flow quantity controlled by the throttle valve. Meanwhile, the first inlet passage is supplied air by the charger.
If the feed volume and/or the feed pressure delivered by the charger can be regulated, the throttle valve and the intake line may be dispensed with. The flow quantity control during some portions of the characteristic engine operation can be through the charger. In an exhaust-gas turbocharger, the feed volume or feed pressure can be regulated by utilising a variable adjustable blade mechanism.
In the case of a charger or supercharger driven mechanically by the engine, the charger""s speed may be regulated via a continuously variable gear drive. If the charger is driven by an electric motor, it is relatively simple to regulate the speed of the electric motor according to desired output requirements.